Acoustic wave filter with acoustic velocity adjustment structure

ABSTRACT

Aspects of this disclosure relate to a surface acoustic wave filter with an acoustic velocity adjustment structure. The surface acoustic wave filter can include a first interdigital transducer electrode disposed on a piezoelectric layer, an acoustic reflector disposed on the piezoelectric layer, and a second interdigital transducer electrode disposed on the piezoelectric layer. The second interdigital transducer electrode is longitudinally coupled to the first interdigital transducer electrode and positioned between the first interdigital transducer electrode and the acoustic reflector. The acoustic velocity adjustment structure can be positioned over at least a gap between the first interdigital transducer electrode and the second interdigital transducer electrode. The acoustic velocity adjustment structure can be arranged to increase an acoustic wave propagation velocity in a first region that includes the gap relative to a second region over at least a portion of the first interdigital transducer electrode.

INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS

Any and all applications for which a foreign or domestic priority claimis identified in the Application Data Sheet as filed with the presentapplication, including U.S. Provisional Patent Application No.62/938,821, filed Nov. 21, 2019, titled “ACOUSTIC WAVE FILTER WITHACOUSTIC VELOCITY ADJUSTMENT STRUCTURE,” U.S. Provisional PatentApplication No. 62/938,838, filed Nov. 21, 2019, titled “ACOUSTIC WAVEDEVICE WITH ACOUSTIC VELOCITY REGIONS,” and U.S. Provisional PatentApplication No. 62/938,782, filed Nov. 21, 2019, titled “ACOUSTIC WAVEDEVICE WITH VELOCITY ADJUSTMENT LAYER,” are hereby incorporated byreference under 37 CFR 1.57 in their entirety.

BACKGROUND Technical Field

Embodiments of this disclosure relate to acoustic wave devices and/oracoustic wave filters with an acoustic velocity adjustment structure.

Description of Related Technology

An acoustic wave filter can include a plurality of resonators arrangedto filter a radio frequency signal. Example acoustic wave filtersinclude surface acoustic wave (SAW) filters and bulk acoustic wave (BAW)filters. A surface acoustic wave resonator can include an interdigitaltransductor electrode on a piezoelectric substrate. The surface acousticwave resonator can generate a surface acoustic wave on a surface of thepiezoelectric layer on which the interdigital transductor electrode isdisposed. A multi-mode SAW filter can include a plurality oflongitudinally coupled interdigital transducer electrodes positionedbetween acoustic reflectors.

Acoustic wave filters can be implemented in radio frequency electronicsystems. For instance, filters in a radio frequency front end of amobile phone can include acoustic wave filters. An acoustic wave filtercan be a band pass filter. A plurality of acoustic wave filters can bearranged as a multiplexer. For example, two acoustic wave filters can bearranged as a duplexer.

SUMMARY

The innovations described in the claims each have several aspects, nosingle one of which is solely responsible for its desirable attributes.Without limiting the scope of the claims, some prominent features ofthis disclosure will now be briefly described.

In one aspect, a multi-mode surface acoustic wave filter is disclosed.The multi-mode surface acoustic wave filter can include a firstinterdigital transducer electrode positioned on a piezoelectric layer,an acoustic reflector positioned on the piezoelectric layer, a secondinterdigital transducer electrode positioned on the piezoelectric layer,and an acoustic velocity adjustment structure positioned over at least agap between the first interdigital transducer electrode and the secondinterdigital transducer electrode. The second interdigital transducerelectrode is longitudinally coupled to the first interdigital transducerelectrode and positioned between the first interdigital transducerelectrode and the acoustic reflector. The acoustic velocity adjustmentstructure is arranged to increase an acoustic wave propagation velocityin a first region that includes the gap relative to a second region overat least a portion of the first interdigital transducer electrode.

In one embodiment, the acoustic velocity adjustment structure includes ahigh speed layer over the first region to increase the acoustic wavepropagation velocity in the first region. The high speed layer caninclude a silicon nitride layer. The high speed layer can include analuminum oxide layer.

In one embodiment, the multi-mode surface acoustic wave filter furtherincludes a temperature compensation layer over the piezoelectric layer.The acoustic velocity adjustment structure can be at least partiallyembedded in the temperature compensation layer. The acoustic velocityadjustment structure can be at least partially disposed on thetemperature compensation layer.

In one embodiment, the second region includes a first sub-region and asecond sub-region. The first sub-region can be defined over at least theportion of the first interdigital transducer electrode. The secondsub-region can be defined over at least a portion of the secondinterdigital transducer electrode. The acoustic wave propagationvelocity in the first sub-region and the acoustic wave propagationvelocity in the second sub-region can be approximately the same.

In one embodiment, the multi-mode surface acoustic wave filter furtherincludes a third region over at least a portion of the acousticreflector. The acoustic velocity adjustment structure can include a lowspeed layer over the third region. The low speed layer can be configuredto decrease the acoustic wave propagation velocity in the third regionrelative to the second region.

In one embodiment, the multi-mode surface acoustic wave filter furtherincludes a third interdigital transducer electrode longitudinallycoupled to the first interdigital transducer electrode such that thefirst interdigital transducer electrode is positioned between the thirdinterdigital transducer electrode and the second interdigital transducerelectrode. The multi-mode surface acoustic wave filter can furtherinclude a second acoustic reflector that is longitudinally arranged suchthat the third interdigital transducer electrode is positioned betweenthe second acoustic reflector and the first interdigital transducerelectrode.

In one embodiment, the first interdigital transducer electrode and thesecond interdigital transducer electrode each has substantially uniformpitch. The first interdigital transducer electrode and the secondinterdigital transducer electrode can have a pitch variation of nogreater than 10 percent. The first interdigital transducer electrode andthe second interdigital transducer electrode can have a pitch variationof no greater than 5 percent.

In one embodiment, the multi-mode surface acoustic wave filter furtherincludes a support substrate on which the piezoelectric layer ispositioned.

In one embodiment, the first region includes a portion of the firstinterdigital transducer electrode. The portion of the first interdigitaltransducer electrode can be less than one third of a length of the firstinterdigital transducer electrode along a direction perpendicular to anaperture direction.

In one aspect, a radio frequency module is disclosed. The radiofrequency module can include a filter that includes any multi-modesurface acoustic wave filter disclosed herein, and a radio frequencycircuit element that is coupled to the filter. The filter and the radiofrequency circuit element are enclosed within a common module package.

In one embodiment, the radio frequency circuit element is a radiofrequency amplifier arranged to amplify a radio frequency signal.

In one embodiment, the radio frequency circuit element is a switchconfigured to selectively couple the filter to a port of the radiofrequency module.

In one aspect, a wireless communication device is disclosed. Thewireless communication device can include a filter that include anymulti-mode surface acoustic wave filter disclosed herein, an antennathat is operatively coupled to the filter, a radio frequency amplifierthat is operatively coupled to the multi-mode surface acoustic wavefilter and a transceiver in communication with the radio frequencyamplifier. The radio frequency amplifier is configured to amplify aradio frequency signal

In one embodiment, the wireless communication device further includes abaseband processor in communication with the transceiver.

In one embodiment, the filter is included in a radio frequency frontend.

In one embodiment, the filter is included in a diversity receive module.

In one aspect, a method of filtering a radio frequency signal isdisclosed. The method can include receiving a radio frequency signal ata port of a filter that includes any multi-mode surface acoustic wavefilter disclosed herein, and filtering the radio frequency signal withthe filter.

In one aspect, a surface acoustic wave device is disclosed. The surfaceacoustic wave device can include a piezoelectric layer and a verticalstack positioned over the piezoelectric layer. The vertical stackincludes a first acoustic reflector positioned on the piezoelectriclayer, a second acoustic reflector positioned on the piezoelectriclayer, and an interdigital transducer electrode positioned on thepiezoelectric layer and positioned between the first acoustic reflectorand the second acoustic reflector. The interdigital transducer electrodehas a first side closer to the first acoustic reflector and a secondside closer to the second acoustic reflector. A vertical arrangement ofthe vertical stack is configured such that an acoustic wave propagationvelocity of a first region between the first side and a first reflectoris faster than an acoustic wave propagation velocity of a second regionbetween the first side and the second side.

In one embodiment, the vertical stack includes a high speed layer overthe first region. The vertical stack can include a temperaturecompensation layer between a portion of the piezoelectric layer and thehigh speed layer. The high speed layer can include a silicon nitridelayer. The high speed layer can include an aluminum oxide layer.

In one embodiment, the vertical stack includes a low speed layer with atrench over the first region.

In one embodiment, the surface acoustic wave device further includes asecond interdigital transducer electrode that is positioned between thefirst side and the first reflector. The second interdigital transducerelectrode can be longitudinally coupled to the first interdigitaltransducer electrode. The surface acoustic wave device can furtherinclude a third interdigital transducer electrode positioned between thesecond side and the second reflector, the third interdigital transducerelectrode being longitudinally coupled to the second interdigitaltransducer electrode. The second region can be in between the first sideand the second interdigital transducer electrode. The second region canoverlap at least a portion of the second interdigital transducerelectrode.

In one embodiment, the second region overlaps at least a portion of theinterdigital transducer electrode.

In one embodiment, an acoustic wave propagation velocity of a thirdregion over the first acoustic reflector is slower than the firstregion. The vertical stack can include a low speed layer positioned overthe first acoustic reflector in the third region, the low speed layerconfigured to decrease the acoustic wave propagation velocity in thethird region. The low speed layer can be a metal layer. The metal layercan include at least one of a molybdenum layer, a copper layer, atungsten layer, a titanium layer, a silver layer, a gold layer, aruthenium layer, or a platinum layer. The low speed layer can be adielectric layer. The dielectric layer can include at least one oftantalum oxide layer or a tellurium dioxide layer.

In one embodiment, the vertical stack includes a high speed layer thatis positioned over at least a portion of the interdigital transducerelectrode in a third region between the second side and the secondacoustic reflector. The high speed layer can be configured to increasethe acoustic wave propagation velocity in the second region. The highspeed layer can include at least one of a silicon nitride layer, siliconoxynitride layer, or aluminum oxide layer. The vertical stack caninclude a temperature compensation layer between a portion of theinterdigital transducer electrode structure and the high speed layer.The vertical stack can include a temperature compensation layerpositioned over the first interdigital transducer electrode.

In one embodiment, the surface acoustic wave device is arranged as amulti-mode surface acoustic wave filter.

In one embodiment, the surface acoustic wave device is arranged as asurface acoustic wave resonator.

In one embodiment, the first acoustic reflector, the second acousticreflector, and the interdigital transducer electrode each hassubstantially uniform pitch. The first acoustic reflector, the secondacoustic reflector, and the interdigital transducer electrode can have apitch variation of no greater than 10 percent. The first acousticreflector, the second acoustic reflector, and the interdigitaltransducer electrode can have a pitch variation of no greater than 5percent.

In one aspect, a radio frequency module is disclosed. the radiofrequency module can include a filter that includes any surface acousticwave device disclosed herein and a radio frequency circuit elementcoupled to the filter. The filter and the radio frequency circuitelement can be enclosed within a common module package.

In one embodiment, the radio frequency circuit element is a radiofrequency amplifier arranged to amplify a radio frequency signal.

In one embodiment, the radio frequency circuit element is a switchconfigured to selectively couple the filter to a port of the radiofrequency module.

In one aspect, a wireless communication device is disclosed. thewireless communication device can include a filter that include anysurface acoustic wave device disclosed herein, an antenna operativelythat is coupled to the filter, a radio frequency amplifier operativelythat is coupled to the acoustic wave filter and configured to amplify aradio frequency signal, and a transceiver that is in communication withthe radio frequency amplifier.

In one embodiment, the wireless communication device further includes abaseband processor in communication with the transceiver.

In one embodiment, the filter is included in a radio frequency frontend.

In one embodiment, the filter is included in a diversity receive module.

In one aspect, a method of filtering a radio frequency signal isdisclosed. the method can include receiving a radio frequency signal ata port of a filter that includes any surface acoustic wave devicedisclosed herein and filtering the radio frequency signal with thefilter.

In one aspect, a surface acoustic wave device is disclosed. The surfaceacoustic wave device can include a piezoelectric layer, a firstreflector positioned over the piezoelectric layer, a second reflectorpositioned over the piezoelectric layer, an interdigital transducerelectrode structure positioned over the piezoelectric layer andpositioned between the first reflector and the second reflector, and ahigh speed layer positioned over at least a portion between the firstside and the first reflector. The interdigital transducer structurehaving a first side closer to the first reflector and a second sidecloser to the second reflector. The high speed layer in positioned suchthat an acoustic wave propagation velocity in a fast region overlappingthe high speed layer is greater than an acoustic wave propagationvelocity a region between the first side and the second side.

In one embodiment, the surface acoustic wave device further includes alow speed layer positioned over the first reflector such that anacoustic wave propagation velocity in a slow region over the firstreflector is slower than in the fast region overlapping the high speedlayer and the region between the first side and the second side. The lowspeed layer and the first reflector can be spaced apart by a temperaturecompensation layer. A portion of the high speed layer and a portion ofthe low speed layer can vertically overlap.

In one embodiment, the surface acoustic wave device is arranged as amulti-mode surface acoustic wave filter. The interdigital transducerelectrode structure can have a pitch variation of less than 10 percent.

In one embodiment, the surface acoustic wave device is a surfaceacoustic wave resonator.

In one aspect, a surface acoustic wave device is disclosed. The surfaceacoustic wave device can include a piezoelectric layer, a firstreflector positioned over the piezoelectric layer, a second reflectorpositioned over the piezoelectric layer, an interdigital transducerelectrode structure positioned over the piezoelectric layer andpositioned between the first reflector and the second reflector, a lowspeed layer positioned in a slow region over the first reflector. Theinterdigital transducer structure has a first side closer to the firstreflector and a second side closer to the second reflector. The lowspeed layer is positioned such that an acoustic wave propagationvelocity of the slow region is slower than an acoustic wave propagationvelocity of a region between the first side and the second side.

In one embodiment, the surface acoustic wave device further includes atemperature compensation layer over the interdigital transducerelectrode, the first reflector, and the second reflector. The low speedlayer and the first reflector can be spaced apart by the temperaturecompensation layer.

In one embodiment, the surface acoustic wave device is arranged as amulti-mode surface acoustic wave filter. The interdigital transducerelectrode structure can have a pitch variation of less than 10 percent.

In one embodiment, the surface acoustic wave device is a surfaceacoustic wave resonator.

In one aspect, a radio frequency module is disclosed. the radiofrequency module can include a filter that includes any surface acousticwave device disclosed herein and a radio frequency circuit element thatis coupled to the filter. The filter and the radio frequency circuitelement are enclosed within a common module package.

In one embodiment, the radio frequency circuit element is a radiofrequency amplifier arranged to amplify a radio frequency signal.

In one embodiment, the radio frequency circuit element is a switchconfigured to selectively couple the filter to a port of the radiofrequency module.

In one aspect, a wireless communication device is disclosed. Thewireless communication device can include a filter that includes anysurface acoustic wave device disclosed herein, an antenna that isoperatively coupled to the filter, a radio frequency amplifier that isoperatively coupled to the acoustic wave filter and configured toamplify a radio frequency signal, and a transceiver that is incommunication with the radio frequency amplifier.

In one embodiment, the wireless communication device further includes abaseband processor in communication with the transceiver.

In one embodiment, the filter is included in a radio frequency frontend.

In one embodiment, the filter is included in a diversity receive module.

In one aspect, a method of filtering a radio frequency signal isdisclosed. The method can include receiving a radio frequency signal ata port of a filter that includes any surface acoustic wave devicedisclosed herein and filtering the radio frequency signal with thefilter.

The present disclosure relates to U.S. patent application Ser. No.______ [Attorney Docket SKYWRKS.993A2], titled “ACOUSTIC WAVE DEVICEWITH ACOUSTIC VELOCITY REGIONS,” filed on even date herewith, the entiredisclosure of which is hereby incorporated by reference herein. Thepresent disclosure relates to U.S. patent application Ser. No.______[Attorney Docket SKYWRKS.993A3], titled “ACOUSTIC WAVE DEVICE WITHVELOCITY ADJUSTMENT LAYER” filed on even date herewith, the entiredisclosure of which is hereby incorporated by reference herein.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of this disclosure will now be described, by way ofnon-limiting example, with reference to the accompanying drawings.

FIG. 1A illustrates a top plan view of a multimode longitudinallycoupled surface acoustic wave (SAW) structure according to oneembodiment.

FIG. 1B illustrates a velocity profile of the SAW structure shown inFIG. 1A.

FIG. 1C illustrates a pitch profile of the SAW structure shown in FIG.1A.

FIG. 2A is a graph that illustrates simulated admittance results of twoSAW filters.

FIG. 2B is another graph that illustrates simulated admittance resultsof the two SAW filters.

FIG. 3A illustrates a cross section of a multimode longitudinallycoupled SAW structure according to one embodiment.

FIG. 3B illustrates a top plan view of the SAW structure illustrated inFIG. 3A.

FIG. 3C illustrates a cross section of a multimode longitudinallycoupled SAW structure according to one embodiment.

FIG. 4A illustrates a cross section of a multimode longitudinallycoupled SAW structure according to one embodiment.

FIG. 4B illustrates a top plan view of the SAW structure illustrated inFIG. 4A.

FIG. 5A illustrates a cross section of a multimode longitudinallycoupled SAW structure according to one embodiment.

FIG. 5B illustrates a top plan view of the SAW structure illustrated inFIG. 5A.

FIG. 6A illustrates a cross section of a multimode longitudinallycoupled SAW structure according to one embodiment.

FIG. 6B illustrates a top plan view of the SAW structure illustrated inFIG. 6A.

FIG. 7A illustrates a cross section of a multimode longitudinallycoupled SAW structure according to one embodiment.

FIG. 7B illustrates a top plan view of the SAW structure illustrated inFIG. 7A.

FIG. 8A illustrates a cross section of a multimode longitudinallycoupled SAW structure according to one embodiment.

FIG. 8B illustrates a top plan view of the SAW structure illustrated inFIG. 8A.

FIG. 9A illustrates a cross section of a multimode longitudinallycoupled SAW structure according to one embodiment.

FIG. 9B illustrates a top plan view of the SAW structure illustrated inFIG. 9A.

FIG. 10A illustrates a cross section of a multimode longitudinallycoupled SAW structure according to one embodiment.

FIG. 10B illustrates a top plan view of the SAW structure illustrated inFIG. 10A.

FIG. 11A illustrates a cross section of a multimode longitudinallycoupled SAW structure according to one embodiment.

FIG. 11B illustrates a top plan view of the SAW structure illustrated inFIG. 11A.

FIG. 12A illustrates a cross section of a multimode longitudinallycoupled SAW structure according to one embodiment.

FIG. 12B illustrates a top plan view of the SAW structure illustrated inFIG. 12A.

FIG. 13A illustrates a cross section of a multimode longitudinallycoupled SAW structure according to one embodiment.

FIG. 13B illustrates a top plan view of the SAW structure illustrated inFIG. 13A.

FIG. 14A illustrates a cross section of a multimode longitudinallycoupled SAW structure according to one embodiment.

FIG. 14B illustrates a top plan view of the SAW structure illustrated inFIG. 14A.

FIG. 15A illustrates a cross section of a ladder SAW structure accordingto one embodiment.

FIG. 15B illustrates a top plan view of the SAW structure illustrated inFIG. 15A.

FIG. 16 is a schematic diagram of an acoustic filter that includesladder stages and a multi-mode surface acoustic wave filter.

FIG. 17 is a schematic diagram of a radio frequency module that includesa surface acoustic wave resonator according to an embodiment.

FIG. 18 is a schematic diagram of a radio frequency module that includesfilters with surface acoustic wave resonators according to anembodiment.

FIG. 19 is a schematic block diagram of a module that includes anantenna switch and duplexers that include a surface acoustic waveresonator according to an embodiment.

FIG. 20A is a schematic block diagram of a module that includes a poweramplifier, a radio frequency switch, and duplexers that include asurface acoustic wave resonator according to an embodiment.

FIG. 20B is a schematic block diagram of a module that includes filters,a radio frequency switch, and a low noise amplifier according to anembodiment.

FIG. 21A is a schematic block diagram of a wireless communication devicethat includes a filter with a surface acoustic wave resonator inaccordance with one or more embodiments.

FIG. 21B is a schematic block diagram of another wireless communicationdevice that includes a filter with a surface acoustic wave resonator inaccordance with one or more embodiments.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

The following description of certain embodiments presents variousdescriptions of specific embodiments. However, the innovations describedherein can be embodied in a multitude of different ways, for example, asdefined and covered by the claims. In this description, reference ismade to the drawings where like reference numerals can indicateidentical or functionally similar elements. It will be understood thatelements illustrated in the figures are not necessarily drawn to scale.Moreover, it will be understood that certain embodiments can includemore elements than illustrated in a drawing and/or a subset of theelements illustrated in a drawing. Further, some embodiments canincorporate any suitable combination of features from two or moredrawings.

Acoustic wave filters can filter radio frequency (RF) signals in avariety of applications, such as in an RF front end of a mobile phone.An acoustic wave filter can be implemented with surface acoustic wave(SAW) devices. A SAW device can be, for example, a multimodelongitudinally coupled SAW filter (e.g., a double mode SAW (DMS) filter)or a SAW resonator.

Multimode SAW (MMS) filters are key structures for meeting certaindesign specifications for radio frequency (RF) filter components. Inorder for an MMS filter to provide a desired frequency response for somedesign specifications, a pitch of an interdigital transducer (IDT)electrode structure can be modulated such that fingers of the IDTstructure are unevenly spaced. However, in some applications, such anMMS filter with varying and/or uneven IDT electrode pitch can lead toradiation losses, for example, due to discontinuity and/or processlimitations for relatively high frequency filter devices. The lossmechanism due to aperiodicity of IDT electrode fingers can be difficultto quantify and/or model. Further, there may be manufacturingdifficulties for manufacturing a SAW device with varying/uneven pitch.There may be manufacturing limitations to forming narrow pitch IDTelectrode fingers in certain manufacturing processes.

Aspects of this disclosure relate to SAW devices (e.g., multimodelongitudinally coupled SAW filters and/or SAW resonators) that canreduce and/or eliminate radiation losses. At the same time, such SAWdevices can provide a desirable frequency response (e.g., a relativelyhigh quality factor (Q) and/or a reduced bulk radiation). Aspects ofthis disclosure relate to SAW devices that include an acoustic velocityadjustment structure. The acoustic velocity adjustment structure caninclude a high speed layer that speeds up an acoustic velocity of asurface acoustic wave generated by the SAW device in a region of the SAWdevice and/or a low speed layer that slows down the acoustic velocity ina region of the SAW device. Positioning of such a velocity adjustmentstructure can create different velocity regions in a SAW devices.

Creating different velocity regions in a SAW device primarily with avelocity adjustment structure implemented in one or more layers above anIDT electrode can reduce one or more loss mechanisms of the SAW devicecompared to a similar SAW device that primarily uses aperiodic IDTelectrode fingers and/or aperiodic acoustic reflector fingers to createdifferent velocity regions. The velocity adjustment layer can be easierto manufacture than aperiodic IDT electrode fingers. MMS filtersdisclosed herein can be implemented with less pitch variation than someprevious MMS filters. With velocity adjustment structures disclosedherein, NMS filters can filter higher frequency signals with the sameIDT electrode line and space process limitations compared to someprevious MNMS filters.

Embodiments of a SAW filter disclosed herein include a first IDTelectrode, a second IDT electrode longitudinally coupled to the firstIDT electrode, and an acoustic reflector that are on a piezoelectriclayer. The SAW filter also includes an acoustic velocity adjustmentstructure over at least a gap between the first IDT electrode and thesecond IDT electrode. This can increase acoustic velocity in a regionover the gap. The acoustic velocity adjustment structure can be arrangedto change acoustic wave propagation velocity in different regions. Theacoustic velocity adjustment structure can include a high speed layerand/or a trench in a low speed layer to increase acoustic velocity in aregion of the SAW filter. The acoustic velocity adjustment structure caninclude a low speed layer and/or a trench in a high speed layer toincrease acoustic velocity in a region of the SAW filter. Differentacoustic velocity regions can alternatively or additionally beimplemented by high speed layers that increase acoustic velocity bydifferent magnitudes and/or low speed layers that decrease acousticvelocity by different magnitudes. The acoustic velocity adjustmentstructure can be included in a vertical stack that is arranged over thepiezoelectric layer and one or more of the IDT electrodes.

Certain embodiments disclosed herein relate to multimode longitudinallycoupled surface acoustic wave filters. Such filters can be referred toas multimode surface acoustic wave (MNMS) filters. MMS filters caninclude a plurality of IDT electrodes that are longitudinally coupled toeach other and positioned between acoustic reflectors. Some MMS filterscan be referred to as double mode surface acoustic wave (DMS) filters.There may be more than two modes of such DMS filters and/or for otherMMS filters.

MNMS filters can have a relatively wide passband due to a combination ofvarious resonant modes. MMS filters can have a balanced (differential)input and/or a balanced output with proper arrangement of IDTs. MNMSfilters can achieve a relatively low loss and a relatively good out ofband rejection.

MNMS filters can be temperature compensated by including a temperaturecompensation layer, such as a silicon dioxide (SiO₂) layer, over IDTelectrodes. Such a temperature compensation layer can cause atemperature coefficient of frequency (TCF) of an MMS filter to be closerto zero. In some applications, an MNMS filter can include a multi-layerpiezoelectric substrate.

In certain applications, MNMS filters can be receive filters arranged tofilter radio frequency signals received by an antenna. MMS filters canbe included in a receive filter that also includes a plurality ofacoustic resonators arranged in a ladder topology.

With acoustic velocity adjustment layers disclosed herein, an MMS filtercan implement different acoustic velocity regions while keeping pitchesin IDT structures substantially uniform or with a relatively smallamount of pitch modulation. The IDT structure can be positioned betweenthe piezoelectric layer and an acoustic velocity adjustment structure.Accordingly, the acoustic velocity adjustment layer can be implementedabove an IDT structure of a SAW device in a vertical stack.

FIG. 1A illustrates a top plan view of a multimode longitudinallycoupled surface acoustic wave filter 1 according to one embodiment. FIG.1B illustrates a velocity profile of the MMS filter 1 shown in FIG. 1A.FIG. 1C illustrates a pitch profile of the MMS filter 1 shown in FIG.1A. Vertical dashed lines between FIGS. 1A, 1B and 1C indicate relativepositions of the illustrated elements.

The NMS filter 1 illustrated in FIG. 1A includes a first interdigitaltransducer electrode 10, a second interdigital transducer electrode 12,a third interdigital transducer electrode 14, a first acoustic reflector16, and a second acoustic reflector 18. The first IDT electrode 10, thesecond IDT electrode 12, and the third IDT electrode 14 arelongitudinally coupled to each other. The first IDT electrode 10, thesecond IDT electrode 12, and the third IDT electrode 14 are positionedbetween the first acoustic reflector 16 and the second acousticreflector 18.

The MNMS filter 1 has a first-velocity region 20, a second-velocityregion 22, and a third-velocity region 24. The SAW structure 1 alsoincludes an acoustic velocity adjustment structure (e.g., a high speedlayer 26 and a low speed layer 28). The acoustic velocity adjustmentstructure is formed over at least a portion of the IDT electrodes of theNMS filter 1.

The second-velocity region 22 has an acoustic wave propagation velocityV2. FIG. 1B shows that, in the illustrated MNMS filter 1, thefirst-velocity region 20 has an acoustic wave propagation velocity V1that is about 1.055*V, and the third-velocity region 24 has an acousticwave propagation velocity V3 that is about 0.87*V. The first-velocityregion 20 corresponds to a region where the high speed layer 26 ispresent and the third-velocity region 24 corresponds to a region wherethe low speed layer 28 is present. The velocity differences between thefirst-velocity region 20, second-velocity region 22, and thethird-velocity region 24 can be created primarily by the high speedlayer 26 and the low speed layer 28.

FIG. 1C shows that the first interdigital transducer electrode 10, thesecond interdigital transducer electrode 12, the third interdigitaltransducer electrode 14, the first acoustic reflector 16, and the secondacoustic reflector 18 have substantially the same pitch. In other words,fingers of the first interdigital transducer electrode 10, the secondinterdigital transducer electrode 12, the third interdigital transducerelectrode 14, the first acoustic reflector 16, and the second acousticreflector 18 are approximately evenly spaced.

FIGS. 2A and 2B are graphs that illustrate simulated admittance resultsof two SAW filters. FIG. 2A shows a curve 30 for a first SAW filter thatincludes the MMS filter 1 illustrated in FIG. 1A and a curve 32 for asecond SAW filter that is pitch modulated. A pitch modulation can beachieved by varying spacings between fingers of IDT electrodes and/oracoustic reflectors of a SAW filter. In contrast to the second SAWfilter, the first SAW filter is not pitch modulated. Unlike the firstSAW filter, the second SAW filter does not have the high speed layer 26or the low speed layer 28. FIG. 2B shows a curve 34 for the first SAWfilter that includes the MMS filter 1 illustrated in FIG. 1A and a curve36 for the second SAW filter that is pitch modulated.

From these curves 30, 32, 34, and 36, it can be observed that similarsimulated admittance results can be obtained from a SAW filter with anacoustic velocity adjustment structure (e.g., a high speed layer 26, anda low speed layer 28) and a SAW filter that is pitch modulated. In somemanufacturing processes, it may be easier to form the acoustic velocityadjustment structure than forming the IDT structures with varying pitch.Therefore, it can be beneficial to be able to adjust the acoustic wavepropagation velocity without modulating the pitch. Moreover, since someloss mechanisms related to pitch modulation may be difficult to simulateand/or model, the MMS filter of 1A may be able to achieve additionalloss improvements that are not reflected in the simulation results shownin FIGS. 2A and 2B.

FIG. 3A illustrates a cross section of an MMS filter 2 according to oneembodiment. FIG. 3B illustrates a top plan view of the MMS filter 2illustrated in FIG. 3A. Vertical dashed lines indicate relativepositions of components between FIGS. 3A and 3B. The MMS filter 2includes a piezoelectric layer 40, an interdigital transducer (IDT)structure 42 on the piezoelectric layer 40, and a temperaturecompensation layer 44 over the IDT structure 42. The MMS filter 2 alsoincludes an acoustic velocity adjustment structure (e.g., a high speedlayer 26 and a low speed layer 28). Further, the MMS filter 2 has afirst-velocity region 20, a second-velocity region 22, and athird-velocity region 24. The piezoelectric layer 40 and the temperaturecompensation layer 44 are omitted from FIG. 3B.

The MMS filter 2 includes the piezoelectric layer 40 and a verticalstack 41 over the piezoelectric layer 40. The vertical stack 41 includesthe IDT structure 42 and the velocity adjustment structure over the IDTstructure 42. The vertical stack 41 is arranged such that acoustic wavepropagation velocity in the first-velocity region 20 is faster than inthe second-velocity region 22. The vertical stack 41 is also arrangedsuch that acoustic wave propagation velocity in the second-velocityregion 22 is faster than in the third-velocity region 24. Accordingly,in the MMS filter 2, the vertical arrangement in the vertical stackcauses different regions to have different acoustic velocities. This isdifferent than changing IDT electrode spacing to adjust acousticvelocity.

The piezoelectric layer 40 can include any suitable piezoelectric layer,such as a lithium niobate (LN) layer or a lithium tantalate (LT) layer.A thickness of the piezoelectric layer 40 can be selected based on awavelength λ or L of a surface acoustic wave generated by the MMS filter2.

The IDT structure 42 includes a first IDT electrode 10, a second IDTelectrode 12, a third IDT electrode 14, a first acoustic reflector 16,and a second acoustic reflector 18. The IDT electrodes 10, 12, and 14are longitudinally coupled to each other. The IDT electrodes 10, 12, and14 have a pitches that can set the wavelength λ or L of a surfaceacoustic wave in the MMS filter 2.

The IDT structure 42 can include any suitable material. For example, IDTstructure 42 can include tungsten (W), aluminum (Al), copper (Cu),magnesium (Mg), titanium (Ti), molybdenum (Mo), the like, or anysuitable combination thereof. The IDT structure 42 may include alloys,such as AlMgCu, AlCu, etc. In some embodiments, one or more of the firstIDT electrode 10, the second IDT electrode 12, the third IDT electrode14, the first acoustic reflector 16, and/or the second acousticreflector 18 can have a multi-layer structure.

The illustrated IDT structure 42 has a substantially uniform pitch. Inother words, the pitch or the spacings between the fingers of the firstIDT electrode 10, the second IDT electrode 12, the third IDT electrode14, the first acoustic reflector 16, and the second acoustic reflector18 of the MMS filter 2 are the same or generally similar. In certainapplications, a variation of the pitch in the IDT structure 42 can bewithin 10 percent (10%) of the pitch. According to some of theseapplications, the variation of the pitch in the IDT structure 42 can bewithin 5% of the pitch.

The acoustic velocity adjustment structure can adjust the acoustic wavepropagation velocity of a surface acoustic wave generated by the MMSfilter 2. The high speed layer 26 can increase the acoustic wavepropagation velocity and the low speed layer 28 can decrease theacoustic wave propagation velocity. Accordingly, the high speed layer 26can define the first-velocity region 20, and the low speed layer 28 candefine the third-velocity region 24.

The high speed layer 26 can be disposed at any suitable location overthe IDT structure 42. As illustrated in FIG. 3A, the high speed layer 26can be disposed on the temperature compensation layer 44. In theillustrated MMS filter 2, the high speed layers 26 are positioned overat least a gap between the first IDT electrode 10 and the second IDTelectrode 12, and a gap between the first IDT electrode 10 and the thirdIDT electrode 14. The high speed layer 26 can overlap with a portion ofthe first IDT electrode 10. For example, each of the high speed layers26 can overlap with up to one third of the IDT electrode 10. Similarly,each of the high speed layers 26 can overlap with a portion of thesecond or third IDT electrode 10.

The high speed layer 26 can include any suitable material that canincrease the acoustic wave propagation velocity. In some embodiments,the high speed layer 26 can include silicon nitride (SiN), aluminumoxide (Al₂O₃), aluminum nitride, like materials, or any suitablecombination thereof. In some embodiments a thickness of the high speedlayer 26 can affect the amount of velocity change by the high speedlayer 26.

The low speed layer 28 can be disposed at any suitable location over theIDT structure 42. As illustrated in FIG. 3A, the low speed layer 28 canbe embedded in the temperature compensation layer 44. In the illustratedMMS filter 2, the low speed layers 28 are positioned over at least thefirst acoustic reflector 16 and the second acoustic reflector 18. Thelow speed layers 28 can also be positioned over a gap between the secondIDT electrode 12 and the first acoustic reflector 16, and a gap betweenthe third IDT electrode 14 and the second acoustic reflector 18. The lowspeed layers 28 can overlap with a portion of the second IDT electrode12 and a portion of the third IDT electrode 14.

The low speed layer 28 can include any suitable material that candecrease the acoustic wave propagation velocity. In some embodiments,the low speed layer 28 can include, metal, such as, molybdenum (Mo),copper (Cu), tungsten (W), titanium (Ti), gold (Au), silver (Ag),ruthenium (Ru), and/or platinum (Pt), and/or dielectric, such as,tantalum (Ta₂O₃), and/or tellurium dioxide (TeO₂). In some embodiments,a thickness of the low speed layer 26 can affect the amount of velocitychange by the low speed layer 26.

The acoustic wave propagation velocity at the first-velocity region 20of the and/or 2 has a velocity v1. The acoustic wave propagationvelocity at the second-velocity region 22 of the SAW structure 2 has avelocity v2. The acoustic wave propagation velocity at thethird-velocity region 24 of the SAW structure 2 has a velocity v3. Thehigh speed layer 26 can increase the velocity v1 at the first-velocityregion 20 relative to the velocity v2 at the second-velocity region 22.The low speed layer 28 can decrease the velocity v3 at thethird-velocity region 24 relative to the velocity v2 at thesecond-velocity region 22. Therefore, the velocity v1 can be greaterthan the velocity v2 and the velocity v3, and the velocity v3 can beslower than the velocity v1 and the velocity v2.

Although the MMS filter 2 illustrated in FIGS. 3A and 3B shows avelocity relationship of v1>v2>v3 between the first-velocity region 20,the second-velocity region 22, and the third-velocity region 24, in someembodiments different velocity regions with different velocityrelationships can alternatively or additionally be implemented.

Further, the same velocity relationships between the first-velocityregion 20, the second-velocity region 22, and the third-velocity region24 can be achieved by some other embodiments of the acoustic velocityadjustment structure disclosed herein, and any suitable combinationthereof. Moreover, in certain embodiments, there may be more regionsand/or sub-regions than what are illustrated in the FIGS. 3A and 3Band/or other illustrated embodiments. For example, there can be four orfive regions that have different acoustic propagation wave velocitiesand/or a region can have sub-regions that have different acousticpropagation wave velocities. FIGS. 3C-14B illustrate embodiments of amultimode longitudinally coupled SAW filters. Any suitable principlesand advantages of these embodiments can be implemented together witheach other and/or with other embodiments.

FIG. 3C illustrates a cross section of an MMS filter 2′ according toanother embodiment. The MMS filter 2′ is like the MMS filter 2 of FIG.3A except that the MMS filter 2′ additionally includes a supportsubstrate 48 on a side of the piezoelectric layer 40 that is opposite tothe IDT electrode structure 42. FIG. 3C illustrates that an acousticvelocity adjustment structure (e.g., the vertical stack 41) can beimplemented in a MMS filter with a multi-layer piezoelectric substrate.In certain applications, the piezoelectric layer 40 can have a thicknessof less than the pitch λ of the IDT electrodes in the MMS filter 2′.

The support substrate 48 can be any suitable substrate layer, such as asilicon layer, a quartz layer, a ceramic layer, a glass layer, a spinellayer, a magnesium oxide spinel layer, a sapphire layer, a diamondlayer, a silicon carbide layer, a silicon nitride layer, an aluminumnitride layer, or the like. As one example, the MMS filter 2′ caninclude a lithium niobate/silicon piezoelectric substrate in certainapplications.

The support substrate 48 can have a relatively high impedance. Anacoustic impedance of the support substrate 48 can be higher than anacoustic impedance of the piezoelectric layer 40. For instance, thesupport substrate 48 can have a higher acoustic impedance than anacoustic impedance of lithium niobate and a higher acoustic impedancethan lithium tantalate. The acoustic impedance of the support substrate48 can be higher than an acoustic impedance of the temperaturecompensation layer 44. The MMS filter 2′ including the piezoelectriclayer 40 on a high impedance support substrate 48, such as siliconsubstrate, can achieve better thermal dissipation compared to a similarMMS filter without the high impedance support substrate 48.

In certain embodiments, an MMS filter can include two or more layers onthe side of the piezoelectric layer 40 that is opposite to the IDTelectrodes 10, 12, 14. In some embodiments, there can be an additionallayer between the piezoelectric layer 40 and the support substrate 48.The additional layer can be a low impedance layer that has a loweracoustic impedance than the support substrate 48. In some embodiments,the additional layer can be a silicon dioxide (SiO2) layer. Theadditional layer can increase adhesion between layers of the multi-layerpiezoelectric substrate. In such applications, the additional layer canbe referred to as an adhesion layer. Alternatively or additionally, theadditional layer can increase heat dissipation in the MMS filterrelative to the MMS filters 2, 2′. In such applications, the additionallayer can be referred to as a heat dissipation layer. The additionallayer can reduce back reflection of the support substrate in certainapplications. In such applications, the additional layer can scatterback reflections by beam scattering. In some instances, the additionallayer can be a polycrystalline spinel layer and the support substrate 48can be a silicon layer.

FIG. 4A illustrates a cross section of an MMS filter 3 according toanother embodiment. FIG. 4B illustrates a top plan view of the MMSfilter 3 illustrated in FIG. 4A. Vertical dashed lines indicate relativepositions of components between FIGS. 4A and 4B. The MMS filter 3includes a piezoelectric layer 40, an interdigital transducer (IDT)structure 42 on the piezoelectric layer 40, and a temperaturecompensation layer 44 over the IDT structure 42. The MMS filter 3 alsoincludes an acoustic velocity adjustment structure (e.g., a low speedlayer 28). Further, the MMS filter 3 has a center region 50 and an outerregion 24. The piezoelectric layer 40 and the temperature compensationlayer 44 are omitted from FIG. 4B. The MMS filter 3 includes a verticalstack 41′ that includes the IDT structure 42 and the low speed layer 28.

The MMS filter 3 is similar to the MMS filter 2 illustrated in FIGS. 3Aand 3B. However, unlike the MMS filter 2 illustrated in FIGS. 3A and 3B,the acoustic velocity adjustment structure in the MMS filter 3 does notinclude the high speed layer 26. Accordingly, in the MMS filter 3, theacoustic propagation wave velocity in the center region 50 can be thesubstantially constant.

The acoustic wave propagation velocity at the center region 50 has avelocity v4. The acoustic wave propagation velocity at the outer region24 of the MMS filter 3 has a velocity v3. The low speed layer 28 candecrease the acoustic propagation wave velocity v3 at the outer region24 relative to the acoustic propagation wave velocity v4 at the centerregion 50.

FIG. 5A illustrates a cross section of an MMS filter 4 according toanother embodiment. FIG. 5B illustrates a top plan view of the MMSfilter 4 illustrated in FIG. 5A. FIGS. 5A and 5B illustrate that ahigher acoustic velocity region can be created by the absence of a lowvelocity layer and/or a trench in a low velocity layer. Vertical dashedlines indicate relative positions of components between FIGS. 5A and 5B.The MMS filter 4 includes a piezoelectric layer 40, an interdigitaltransducer (IDT) structure 42 on the piezoelectric layer 40, and atemperature compensation layer 44 over the IDT structure 42. The MMSfilter 4 also includes an acoustic velocity adjustment structure (e.g.,a low speed layer 28 and a second low speed layer 52). Further, the MMSfilter 4 has a first-velocity region 20, a second-velocity region 22,and a third-velocity region 24. The piezoelectric layer 40 and thetemperature compensation layer 44 are omitted from FIG. 4B. The MMSfilter 4 includes a vertical stack 41″ that includes the IDT structure42, the low speed layer 28, and the second low speed layer 52.

The MMS filter 4 is similar to the MMS filter 3 illustrated in FIGS. 4Aand 4B. However, unlike the MMS filter 3 illustrated in FIGS. 4A and 4B,the acoustic velocity adjustment structure in the MMS filter 4 includesthe second low speed layer 52. In some embodiments, the low speed layer28 and the second low speed layer 52 can include different materials. Insome embodiments, the low speed layer 28 and the second low speed layer52 can have different thicknesses.

The acoustic wave propagation velocity at the first-velocity region 20of the MMS filter 4 has a velocity v1. The acoustic wave propagationvelocity at the second-velocity region 22 of the MMS filter 4 has avelocity v2. The acoustic wave propagation velocity at thethird-velocity region 24 of the MMS filter 4 has a velocity v3. The lowspeed layer 28 can decrease the velocity v3 at the third-velocity region24 relative to the velocity v1 at the first-velocity region 20. Thesecond low speed layer 52 can decrease the velocity v2 at thesecond-velocity region 22 relative to the velocity v1 at thefirst-velocity region 20. The low speed layer 28 and the second lowspeed layer 52 can be selected such that the velocity v2 at thesecond-velocity region 22 is greater than the velocity v3 at thethird-velocity region 24. Therefore, the velocity v1 can be greater thanthe velocity v2 and the velocity v3, and the velocity v3 can be slowerthan the velocity v1 and the velocity v2.

Although the first-velocity region 20 is free from a low velocity layerin the MMS filter 4, the velocity regions with the relative acousticvelocity relationships achieved by the MMS filter 4 can be achieved witha low speed layer over the first-velocity region 20 that is thinner thatthe illustrated low speed layers and of a suitable material. Moreover,in some applications, a third low speed layer over the first-velocityregion 20 that decreases acoustic velocity less than the low speedlayers 28 and 52 can achieve similar relative acoustic velocityrelationships in regions of a SAW device.

FIG. 6A illustrates a cross section of an MMS filter 5 according toanother embodiment. FIG. 6B illustrates a top plan view of the MMSfilter 5 illustrated in FIG. 6A. Vertical dashed lines indicate relativepositions of components between FIGS. 6A and 6B. The MMS filter 5includes a piezoelectric layer 40, an interdigital transducer (IDT)structure 42 on the piezoelectric layer 40, and a temperaturecompensation layer 44 over the IDT structure. The MMS filter 5 alsoincludes an acoustic velocity adjustment structure (e.g., a high speedlayer 26). Further, the MMS filter 5 has a first-velocity region 20, asecond-velocity region 22, and a third-velocity region 25. Thepiezoelectric layer 40 and the temperature compensation layer 44 areomitted from FIG. 6B. The MMS filter 5 includes a vertical stack 41′″that includes the IDT structure 42 and the high speed layer 26.

The MMS filter 5 is similar to the MMS filter 2 illustrated in FIGS. 3Aand 3B. However, unlike the MMS filter 2 illustrated in FIGS. 3A and 3B,the acoustic velocity adjustment structure in the MMS filter 5 does notinclude the low speed layer 28. Accordingly, in the MMS filter 5, theacoustic propagation wave velocity of at the second-velocity region 22and the third-velocity region 25 can be approximately the same.

The acoustic wave propagation velocity at the first-velocity region 20of the MMS filter 5 has a velocity v1. The acoustic wave propagationvelocity at the second-velocity region 22 of the MMS filter 5 has avelocity v2. The acoustic wave propagation velocity at thethird-velocity region 25 of the MMS filter 5 has a velocity v2. The highspeed layer 26 can increase the velocity v1 at the first-velocity region20 relative to the velocity v2 at the second-velocity region 22 and/orthe velocity v2 at the third-velocity region 25. Therefore, the velocityv1 can be greater than the velocity v2.

FIG. 7A illustrates a cross section of an MMS filter 6 according toanother embodiment. FIG. 7B illustrates a top plan view of the MMSfilter 6 illustrated in FIG. 7A. Vertical dashed lines indicate relativepositions of components between FIGS. 7A and 7B. The MMS filter 6includes a piezoelectric layer 40, an interdigital transducer (IDT)structure 42 on the piezoelectric layer 40, and a temperaturecompensation layer 44 over the IDT structure 42. The MMS filter 6 alsoincludes an acoustic velocity adjustment structure (e.g., a high speedlayer 26 and a second high speed layer 54). Further, the MMS filter 6has a first-velocity region 20, a second-velocity region 22, and athird-velocity region 24. The piezoelectric layer 40 and the temperaturecompensation layer 44 are omitted from FIG. 7B. The MMS filter 6includes a vertical stack 41″″ that includes the IDT structure 42, thehigh speed layer 26, and the second high speed layer 54.

The MMS filter 6 is similar to the MMS filter 5 illustrated in FIGS. 6Aand 6B. However, unlike the MMS filter 5 illustrated in FIGS. 6A and 6B,the acoustic velocity adjustment structure in the MMS filter 6 includesthe second high speed layer 54. In some embodiments, the high speedlayer 26 and the second high speed layer 54 can include differentmaterials. In some other embodiments, the high speed layer 26 and thesecond high speed layer 54 can have different thicknesses.

The acoustic wave propagation velocity at the first-velocity region 20of the MMS filter 6 has a velocity v1. The acoustic wave propagationvelocity at the second-velocity region 22 of the MMS filter 6 has avelocity v2. The acoustic wave propagation velocity at thethird-velocity region 24 of MMS filter 6 has a velocity v3. The highspeed layer 26 can increase the velocity v1 at the first-velocity region20 relative to the velocity v3 at the third-velocity region 24. Thesecond high speed layer 54 can increase the velocity v2 at thesecond-velocity region 22 relative to the velocity v3 at thethird-velocity region 24. The high speed layer 26 and the second highspeed layer 54 can be selected such that the velocity v1 at thefirst-velocity region 20 is greater than the velocity v2 at thesecond-velocity region 22. Therefore, the velocity v1 can be greaterthan the velocity v2 and the velocity v3, and the velocity v3 can beslower than the velocity v and the velocity v2 in the MMS filter 6.

FIG. 8A illustrates a cross section of an MMS filter 7 according toanother embodiment. FIG. 8B illustrates a top plan view of the MMSfilter 7 illustrated in FIG. 8A. Vertical dashed lines indicate relativepositions of components between FIGS. 8A and 8B. The MMS filter 7includes a piezoelectric layer 40, an interdigital transducer (IDT)structure 42 on the piezoelectric layer 40, a temperature compensationlayer 44 over the IDT structure 42, and a passivation layer 56. The MMSfilter 7 also includes an acoustic velocity adjustment structure (e.g.,a high speed layer 26 and a low speed layer 28). Further, the MMS filter7 has a first-velocity region 20, a second-velocity region 22, and athird-velocity region 24. The piezoelectric layer 40, the temperaturecompensation layer 44, and the passivation layer 56 are omitted fromFIG. 8B. The MMS filter 7 includes a vertical stack 41′″ that includesthe IDT structure 42, the high speed layer 26, and a low speed layer 28.

The MMS filter 7 is similar to the MMS filter 2 illustrated in FIGS. 3Aand 3B. However, unlike the MMS filter 2 illustrated in FIGS. 3A and 3B,the MMS filter 7 includes the passivation layer 56. In FIG. 8A, thepassivation layer 56 is disposed on the temperature compensation layer44, and the high speed layer 26 is positioned on the passivation layer56. However, in some other embodiments, the high speed layer 26 can bepositioned between the temperature compensation layer 44 and thepassivation layer 56.

The illustrated passivation layer 56 is disposed entirely over an uppersurface of the temperature compensation layer 44 in the illustratedcross section. However, the passivation layer 56 can be disposedpartially over the upper surface of the temperature compensation layer44 with one or more trenches, in some other instances. In someembodiments, the passivation layer 56 can be a dispersion adjustmentlayer. The dispersion adjustment layer can cause a magnitude of thevelocity in the underlying region of the MMS filter 7 to be increased.In certain applications, the passivation layer 56 can include anysuitable material to increase the magnitude of the velocity of theunderlying region of the MMS filter 7. According in some applications,the passivation layer 56 can include silicon nitride (SiN). In someembodiments, the passivation layer 56 can be patterned such that theacoustic propagation velocity can be adjusted at certain regions of theMMS filter 7. For example, the passivation layer 56 can have a trench.

In some instances, the passivation layer 56 can physically protect theMMS filter 7. In some instances, the passivation layer 56 can be usedfor frequency trimming and/or frequency tuning. The passivation layer 56can include a silicon nitride (SiN) layer and/or an aluminum oxide(Al₂O₃) layer.

FIG. 9A illustrates a cross section of an MMS filter 8 according toanother embodiment. FIG. 9B illustrates a top plan view of the MMSfilter 8 illustrated in FIG. 9A. Vertical dashed lines indicate relativepositions of components between FIGS. 9A and 9B. The MMS filter 8includes a piezoelectric layer 40, an interdigital transducer (IDT)structure 42 on the piezoelectric layer 40, a temperature compensationlayer 44 over the IDT structure 42, and a passivation layer 56. The MMSfilter 8 also includes an acoustic velocity adjustment structure (e.g.,a high speed layer 26 and a low speed layer 28). Further, MMS filter 8has a first-velocity region 20, a second-velocity region 22, and athird-velocity region 24. The piezoelectric layer 40, the temperaturecompensation layer 44, and the passivation layer 56 are omitted fromFIG. 8B. The MMS filter 8 includes a vertical stack 41″″″ that includesthe IDT structure 42, the high speed layer 26, and the low speed layer28.

The MMS filter 8 is similar to the MMS filter 7 illustrated in FIGS. 8Aand 8B. However, unlike the MMS filter 7 illustrated in FIGS. 8A and 8B,the low speed layer 28 is disposed over the passivation layer 56.

FIG. 10A illustrates a cross section of an MMS filter 9 according toanother embodiment. FIG. 10B illustrates a top plan view of the MMSfilter 9 illustrated in FIG. 10A. Vertical dashed lines indicaterelative positions of components between FIGS. 10A and 10B. The MMSfilter 9 includes a piezoelectric layer 40, an interdigital transducer(IDT) structure 42 on the piezoelectric layer 40, and a temperaturecompensation layer 44 over the IDT structure 42. The MMS filter 9 alsoincludes an acoustic velocity adjustment structure (e.g., a high speedlayer 26 and a low speed layer 28). Further, the MMS filter 9 has afirst-velocity region 20, a second-velocity region 22, a third-velocityregion 24, and a fourth-velocity region 58. The piezoelectric layer 40,the temperature compensation layer 44, and the passivation layer 56 areomitted from FIG. 10B. The MMS filter 9 includes a vertical stack 41′″″″that includes the IDT structure 42, the high speed layer 26, and the lowspeed layer 28.

The high speed layers 26 are positioned over at least gaps between thefirst IDT electrode 10 and the second IDT electrode 12, and the firstIDT electrode 10 and the third IDT electrode 14. The high speed layers26 are positioned also over at least a portion of the first IDTelectrode 10, a portion of the second IDT electrode 12, and a portion ofthe third IDT electrode 14. The fourth-velocity region 58 can be definedat least in part by a portion where the high speed layer 26 and the lowspeed layer 28 overlap.

The acoustic wave propagation velocity at the first-velocity region 20of the MMS filter 9 has a velocity v1. The acoustic wave propagationvelocity at the second-velocity region 22 of the MMS filter 9 has avelocity v2. The acoustic wave propagation velocity at thethird-velocity region 24 of the MMS filter 9 has a velocity v3. Theacoustic wave propagation velocity at the fourth-velocity region 58 ofthe MMS filter 9 has a velocity v5. The high speed layer 26 can increasethe velocity v1 at the first-velocity region 20 and the velocity v5 atthe fourth-velocity region 58 relative to the velocity v2 at thesecond-velocity region 22. The low speed layer 28 can decrease thevelocity v3 at the third-velocity region 24 relative to the velocity v2at the second-velocity region 22.

In some embodiments, the high speed layer 26 and the low speed layer 28can cancel out at least some of their effects at the portion where thehigh speed layer 26 and the low speed layer 28 overlap. In someembodiments, the high speed layer 26 and the low speed layer 28 cancancel out their effects at the portion where the high speed layer 26and the low speed layer 28 overlap, such that the velocity v2 at thesecond-velocity region 22 and the velocity v5 at the fourth-velocityregion 58 can be the same or generally similar. The high speed layer 26and the second high speed layer 54 can be selected such that thevelocity v1 at the first-velocity region 20 is greater than the velocityv2 at the second-velocity region 22 and the velocity v5 of thefourth-velocity region 58, and the velocity v3 at the third-velocityregion is slower than the velocity v2 at the second-velocity region 22and the velocity v5 of the fourth-velocity region 58.

FIG. 11A illustrates a cross section of an MMS filter 11 according toanother embodiment. FIG. 11B illustrates a top plan view of the MMSfilter 11 illustrated in FIG. 11A. Vertical dashed lines indicaterelative positions of components between FIGS. 11A and 11B. The MMSfilter 11 includes a piezoelectric layer 40, an interdigital transducer(IDT) structure 42 on the piezoelectric layer 40, and a passivationlayer 56 over the IDT structure 42. The MMS filter 11 also includes anacoustic velocity adjustment structure (e.g., a high speed layer 26 anda low speed layer 28). Further, the MMS filter 11 has a first-velocityregion 20, a second-velocity region 22, a third-velocity region 24, anda fourth-velocity region 58. The piezoelectric layer 40, the temperaturecompensation layer 44, and the passivation layer 56 are omitted fromFIG. 11B. The high speed layer 28 and the low speed layer 26 arepositioned over the passivation layer 56 in the MMS filter 11. The MMSfilter 5 includes a vertical stack 41″″″″ that includes the IDTstructure 42 and the high speed layer 26.

An acoustic velocity adjustment structure positioned over an IDTstructure can adjust acoustic velocity in different acoustic velocityregions of a SAW device. Alternatively or additionally, IDT electrodethickness and/or material can be used to create different acousticvelocity regions in a SAW device. The IDT structure is another structurein the vertical stack 41′″″″″ over the piezoelectric layer 40 that cancontribute to different acoustic velocities in different regions of aSAW device.

FIG. 12A illustrates a cross section of an MMS filter 13 according toanother embodiment. FIG. 12B illustrates a top plan view of the MMSfilter 13 illustrated in FIG. 12A. Vertical dashed lines indicaterelative positions of components between FIGS. 12A and 12B. The MMSfilter 13 includes a piezoelectric layer 40, an interdigital transducer(IDT) structure 42′ on the piezoelectric layer 40, and a temperaturecompensation layer 44 over the IDT structure 42′. The MMS filter 13 alsoincludes an acoustic velocity adjustment structure (e.g., a high speedlayer 26 and a low speed layer 28). Further, the MMS filter 13 has afirst-velocity region 20, a second-velocity region 22, and athird-velocity region 24. The piezoelectric layer 40 and the temperaturecompensation layer 44 are omitted from FIG. 12B. The MMS filter 13includes a vertical stack 41′″″″″ that includes the IDT structure 42,the high speed layer 26, and the low speed layer 28.

The MMS filter 13 is similar to the MMS filter 2 illustrated in FIGS. 3Aand 3B. However, unlike the MMS filter 2 illustrated in FIGS. 3A and 3B,the IDT structure 42′ of the MMS filter 13 has different thicknesses orheights. The first, second, and third IDT electrodes 10, 12, 14 of theMMS filter 13 have thicknesses that are thinner than thicknesses of thefirst acoustic reflector 16′ and the second acoustic reflector 18′. Thethicker first and the second acoustic reflectors 16′ and 18′ can aiddecreasing the velocity v3 at the third-velocity region 24. The similareffect may be obtained by using a different material for the first andthe second acoustic reflectors 16′ and 18′ from the material of the IDTelectrodes 10, 12, and 14. For example, the first and the secondacoustic reflectors 16′ and 18′ may have a heavier and/or more densematerial than the material of the IDT electrodes 10, 12, 14, in whichthe heavier and/or more dense material causes a reduction in acousticvelocity.

FIG. 13A illustrates a cross section of an MMS filter 15 according toanother embodiment. FIG. 13B illustrates a top plan view of the MMSfilter 15 illustrated in FIG. 13A. Vertical dashed lines indicaterelative positions of components between FIGS. 13A and 13B. The MMSfilter 15 includes a piezoelectric layer 40, an interdigital transducer(IDT) structure 42″ on the piezoelectric layer 40, and a temperaturecompensation layer 44 over the IDT structure 42″. The MMS filter 15 alsoincludes an acoustic velocity adjustment structure (e.g., a low speedlayer 28). Further, the MMS filter 15 has a first-velocity region 20, asecond-velocity region 22, and a third-velocity region 24. Thepiezoelectric layer 40 and the temperature compensation layer 44 areomitted from FIG. 13B. The MMS filter 15 includes a vertical stack41″″″″″ that includes the IDT structure 42 and the low speed layer 28.

The MMS filter 15 is similar to the MMS filter 13 illustrated in FIGS.12A and 12B. However, unlike the MMS filter 13 illustrated in FIGS. 12Aand 12B, the first, second, and third IDT electrodes 10′, 12′, 14′ havedifferent thicknesses or heights, and the high speed layer 26 is omittedin the MMS filter 15. The first, second, and third IDT electrodes 10′,12′, 14′ of the MMS filter 15 have thicker portions at thesecond-velocity region(s) 22.

The acoustic wave propagation velocity at the first-velocity region 20of the MMS filter 15 has a velocity v1. The acoustic wave propagationvelocity at the second-velocity region 22 of the MMS filter 15 has avelocity v2. The acoustic wave propagation velocity at thethird-velocity region 24 of the MMS filter 15 has a velocity v3. Thevelocity v2 at the second-velocity region is decreased relative to thevelocity v1 at the first-velocity region 20 by the thicker portions ofthe first, second, and third IDT electrodes 10′, 12′, 14′ of the MMSfilter 15. The velocity v3 at the third-velocity region 24 is decreasedrelative to the velocity v1 of the first-velocity region 20 by thethicker acoustic reflectors 16′, 18′ and the low speed layer 28.Therefore, the velocity v1 can be greater than the velocity v2 and thevelocity v3, and the velocity v3 can be slower than the velocity v1 andthe velocity v2 in the MMS filter 15.

Although some MMS filters disclosed herein include three longitudinallycoupled IDT electrodes, an MMS filter in accordance with any suitableprinciples and advantages disclosed herein can include any othersuitable number of longitudinally coupled IDT electrodes. FIG. 14Aillustrates a cross section of an MMS filter 17 according to anotherembodiment. FIG. 14B illustrates a top plan view of the MMS filter 17illustrated in FIG. 14A. Vertical dashed lines indicate relativepositions of components between FIGS. 14A and 14B. The MMS filter 17includes a piezoelectric layer 40, an interdigital transducer (IDT)structure 64 on the piezoelectric layer 40, a temperature compensationlayer 44 over the IDT structure 64, and a passivation layer 56. The MMSfilter 17 also includes an acoustic velocity adjustment structure (e.g.,a high speed layer 26 and a low speed layer 28). Further, the MMS filter17 has a first-velocity region 20, a second-velocity region 22, and athird-velocity region 24. The piezoelectric layer 40 and the temperaturecompensation layer 44 are omitted from FIG. 14B. The MMS filter 17includes a vertical stack 41′″″″″″ that includes the IDT structure 42,the high speed layer 26, and a low speed layer 28.

The MMS filter 17 is similar to the MMS filter 2 illustrated in FIGS. 3Aand 3B. However, unlike the MMS filter 2 illustrated in FIGS. 3A and 3B,the IDT structure 64 of the MMS filter 17 includes a fourth IDTelectrode 60 and a fifth IDT electrode 62. The illustrated IDT structure64 includes five longitudinally coupled IDT electrodes 10, 12 14, 60,and 62 positioned between acoustic reflectors 16 and 18. In the MMSfilter 17, the first-velocity region 20 can also include gaps betweenthe second IDT electrode 12 and the fourth IDT electrode 60, and betweenthe third IDT electrode 14 and the fifth IDT electrode 62.

The acoustic wave propagation velocity at the first-velocity region 20of the MMS filter 17 has a velocity v1. The acoustic wave propagationvelocity at the second-velocity region 22 of the MMS filter 17 has avelocity v2. The acoustic wave propagation velocity at thethird-velocity region 24 of the MMS filter 17 has a velocity v3. Thehigh speed layer 26 can increase the velocity v1 at the first-velocityregion 20 relative to the velocity v2 at the second-velocity region 22.The low speed layer 28 can decrease the velocity v3 at thethird-velocity region 24 relative to the velocity v2 at thesecond-velocity region 22. Therefore, the velocity v1 can be greaterthan the velocity v2 and the velocity v3, and the velocity v3 can beslower than the velocity v1 and the velocity v2 in the MMS filter 17.

Although some embodiments disclosed herein related to MMS filters, anysuitable principles and advantages disclosed herein can be implementedin a SAW resonator. FIG. 15A illustrates a cross section of a SAWresonator 19 according to one embodiment. FIG. 15B illustrates a topplan view of the SAW resonator 19 illustrated in FIG. 15A. Verticaldashed lines indicate relative positions of components between FIGS. 15Aand 15B. The SAW resonator 19 includes a piezoelectric layer 40, aninterdigital transducer (IDT) structure 66 on the piezoelectric layer40, a temperature compensation layer 44 over the IDT structure 66, and apassivation layer 56. The IDT structure 66 includes an IDT electrode 68,a first acoustic reflector 16, and a second acoustic reflector 18. TheIDT electrode 68 has a first side closer to the first acoustic reflector16, and a second side closer to the second acoustic reflector 18. TheMMS filter 17 also includes an acoustic velocity adjustment structure(e.g., a high speed layer 26 and a low speed layer 28). Further, the SAWresonator 19 has a first-velocity region 20, a second-velocity region22, and a third-velocity region 24. The piezoelectric layer 40, thetemperature compensation layer 44, and the passivation layer 56 areomitted from FIG. 15B. The SAW resonator 19 includes a vertical stack41″″″″ that includes the IDT structure 42, the high speed layer 26, anda low speed layer 28.

The high speed layers 26 are positioned over at least a portion betweenthe first side of the IDT electrode 68 and the first acoustic reflector16, and between the second side of the IDT electrode 68 and the secondacoustic reflector 18. The high speed layer 26 can overlap with at leasta portion of the IDT electrode 68. For example, the high speed layer 26can overlap with less than one third of the IDT electrode 68.

The acoustic wave propagation velocity at the first-velocity region 20of the SAW resonator 19 has a velocity v1. The acoustic wave propagationvelocity at the second-velocity region 22 of the SAW resonator 19 has avelocity v2. The acoustic wave propagation velocity at thethird-velocity region 24 of the SAW resonator 19 has a velocity v3. Thehigh speed layer 26 can increase the velocity v1 at the first-velocityregion 20 relative to the velocity v2 at the second-velocity region 22.The low speed layer 28 can decrease the velocity v3 at thethird-velocity region 24 relative to the velocity v2 at thesecond-velocity region 22. Therefore, the velocity v1 can be greaterthan the velocity v2 and the velocity v3, and the velocity v3 can beslower than the velocity v1 and the velocity v2 in the SAW resonator 19.

An MMS filter and/or a SAW resonator including any suitable combinationof features disclosed herein be included in a filter arranged to filtera radio frequency signal in a fifth generation (5G) New Radio (NR)operating band within Frequency Range 1 (FR1). A filter arranged tofilter a radio frequency signal in a 5G NR operating band can includeone or more MPS SAW resonators disclosed herein. FR1 can be from 410 MHzto 7.125 GHz, for example, as specified in a current 5G NRspecification. MMS filters disclosed herein can be implemented with lesspitch variation than some previous MMS filters. MMS filters disclosedherein can filter higher frequency signals with the same IDT electrodeline and space process limitations compared to some previous MMSfilters. Filtering higher frequency signals can be advantageous in 5Gapplications. One or more MMS filters and/or SAW resonators inaccordance with any suitable principles and advantages disclosed hereincan be included in a filter arranged to filter a radio frequency signalin a fourth generation (4G) Long Term Evolution (LTE) operating bandand/or in a filter having a passband that includes a 4G LTE operatingband and a 5G NR operating band.

FIG. 16 is a schematic diagram of an acoustic filter 110 that includesladder stages and a multi-mode surface acoustic wave filter 112. Theillustrated acoustic filter 110 includes series resonators R2 and R4,shunt resonators R1 and R3, and multi-mode surface acoustic wave filter112. The filter 110 can be a receive filter. The multi-mode surfaceacoustic wave filter 112 can be connected to a receive port. Themulti-mode surface acoustic wave filter 112 includes longitudinallycoupled IDT electrodes. The multi-mode surface acoustic wave filter 112can include a temperature compensation layer over longitudinally coupledIDT electrodes in certain applications. Alternatively or additionally,the multi-mode surface acoustic wave filter 112 can include amulti-layer piezoelectric substrate in certain applications.

Although FIG. 16 illustrates an example filter topology, any suitablefilter topology can include a SAW device in accordance with any suitableprinciples and advantages disclosed herein. Example filter topologies,include a ladder topology, a lattice topology, a hybrid ladder andlattice topology, a multi-mode SAW filter, a multi-mode SAW filtercombined with one or more other SAW resonators, and the like.

FIG. 17 is a schematic diagram of a radio frequency module 175 thatincludes a surface acoustic wave component 176 according to anembodiment. The illustrated radio frequency module 175 includes the SAWcomponent 176 and other circuitry 177. The SAW component 176 can includeone or more SAW devices with any suitable combination of features of theSAW devices disclosed herein. The SAW component 176 can include a SAWdie that includes one or more MMS filters and/or one or more SAWresonators.

The SAW component 176 shown in FIG. 17 includes a filter 178 andterminals 179A and 179B. The filter 178 includes SAW devices. One ormore of the SAW devices can be implemented in accordance with anysuitable principles and advantages of the MMS filter 1 of FIG. 1A and/orany MNMS filter disclosed herein. The terminals 179A and 178B can serve,for example, as an input contact and an output contact. The SAWcomponent 176 and the other circuitry 177 are on a common packagingsubstrate 180 in FIG. 17. The package substrate 180 can be a laminatesubstrate. The terminals 179A and 179B can be electrically connected tocontacts 181A and 181B, respectively, on the packaging substrate 180 byway of electrical connectors 182A and 182B, respectively. The electricalconnectors 182A and 182B can be bumps or wire bonds, for example. Theother circuitry 177 can include any suitable additional circuitry. Forexample, the other circuitry can include one or more one or more poweramplifiers, one or more radio frequency switches, one or more additionalfilters, one or more low noise amplifiers, the like, or any suitablecombination thereof. The radio frequency module 175 can include one ormore packaging structures to, for example, provide protection and/orfacilitate easier handling of the radio frequency module 175. Such apackaging structure can include an overmold structure formed over thepackaging substrate 180. The overmold structure can encapsulate some orall of the components of the radio frequency module 175.

FIG. 18 is a schematic diagram of a radio frequency module 184 thatincludes a surface acoustic wave device according to an embodiment. Asillustrated, the radio frequency module 184 includes duplexers 185A to185N that include respective transmit filters 186A1 to 186N1 andrespective receive filters 186A2 to 186N2, a power amplifier 187, aselect switch 188, and an antenna switch 189. In some instances, themodule 184 can include one or more low noise amplifiers configured toreceive a signal from one or more receive filters of the receive filters186A2 to 186N2. The radio frequency module 184 can include a packagethat encloses the illustrated elements. The illustrated elements can bedisposed on a common packaging substrate 180. The packaging substratecan be a laminate substrate, for example.

The duplexers 185A to 185N can each include two acoustic wave filterscoupled to a common node. The two acoustic wave filters can be atransmit filter and a receive filter. As illustrated, the transmitfilter and the receive filter can each be band pass filters arranged tofilter a radio frequency signal. One or more of the transmit filters186A1 to 186N1 can include one or more SAW devices in accordance withany suitable principles and advantages disclosed herein. Similarly, oneor more of the receive filters 186A2 to 186N2 can include one or moreSAW devices in accordance with any suitable principles and advantagesdisclosed herein. Although FIG. 18 illustrates duplexers, any suitableprinciples and advantages disclosed herein can be implemented in othermultiplexers (e.g., quadplexers, hexaplexers, octoplexers, etc.) and/orin switch-plexers and/or to standalone filters.

The power amplifier 187 can amplify a radio frequency signal. Theillustrated switch 188 is a multi-throw radio frequency switch. Theswitch 188 can electrically couple an output of the power amplifier 187to a selected transmit filter of the transmit filters 186A1 to 186N1. Insome instances, the switch 188 can electrically connect the output ofthe power amplifier 187 to more than one of the transmit filters 186A1to 186N1. The antenna switch 189 can selectively couple a signal fromone or more of the duplexers 185A to 185N to an antenna port ANT. Theduplexers 185A to 185N can be associated with different frequency bandsand/or different modes of operation (e.g., different power modes,different signaling modes, etc.).

FIG. 19 is a schematic block diagram of a module 190 that includesduplexers 191A to 191N and an antenna switch 192. One or more filters ofthe duplexers 191A to 191N can include any suitable number of surfaceacoustic wave devices in accordance with any suitable principles andadvantages discussed herein. Any suitable number of duplexers 191A to191N can be implemented. The antenna switch 192 can have a number ofthrows corresponding to the number of duplexers 191A to 191N. Theantenna switch 192 can electrically couple a selected duplexer to anantenna port of the module 190. MMS filters disclosed herein can beimplemented in receive filters of one or more of the duplexers 191A to191N, for example.

FIG. 20A is a schematic block diagram of a module 210 that includes apower amplifier 212, a radio frequency switch 214, and duplexers 191A to191N in accordance with one or more embodiments. The power amplifier 212can amplify a radio frequency signal. The radio frequency switch 214 canbe a multi-throw radio frequency switch. The radio frequency switch 214can electrically couple an output of the power amplifier 212 to aselected transmit filter of the duplexers 191A to 191N. One or morefilters of the duplexers 191A to 191N can include any suitable number ofsurface acoustic wave devices in accordance with any suitable principlesand advantages discussed herein. Any suitable number of duplexers 191Ato 191N can be implemented.

FIG. 20B is a schematic block diagram of a module 215 that includesfilters 216A to 216N, a radio frequency switch 217, and a low noiseamplifier 218 according to an embodiment. One or more filters of thefilters 216A to 216N can include any suitable number of MMS filtersand/or acoustic wave resonators in accordance with any suitableprinciples and advantages disclosed herein. Any suitable number offilters 216A to 216N can be implemented. The illustrated filters 216A to216N are receive filters. In some embodiments (not illustrated), one ormore of the filters 216A to 216N can be included in a multiplexer thatalso includes a transmit filter. The radio frequency switch 217 can be amulti-throw radio frequency switch. The radio frequency switch 217 canelectrically couple an output of a selected filter of filters 216A to216N to the low noise amplifier 218. In some embodiments (notillustrated), a plurality of low noise amplifiers can be implemented.The module 215 can include diversity receive features in certainapplications.

FIG. 21A is a schematic diagram of a wireless communication device 220that includes filters 223 in a radio frequency front end 222 accordingto an embodiment. The filters 223 can include one or more SAW devices inaccordance with any suitable principles and advantages discussed herein.The wireless communication device 220 can be any suitable wirelesscommunication device. For instance, a wireless communication device 220can be a mobile phone, such as a smart phone. As illustrated, thewireless communication device 220 includes an antenna 221, an RF frontend 222, a transceiver 224, a processor 225, a memory 226, and a userinterface 227. The antenna 221 can transmit/receive RF signals providedby the RF front end 222. Such RF signals can include carrier aggregationsignals. Although not illustrated, the wireless communication device 220can include a microphone and a speaker in certain applications.

The RF front end 222 can include one or more power amplifiers, one ormore low noise amplifiers, one or more RF switches, one or more receivefilters, one or more transmit filters, one or more duplex filters, oneor more multiplexers, one or more frequency multiplexing circuits, thelike, or any suitable combination thereof. The RF front end 222 cantransmit and receive RF signals associated with any suitablecommunication standards. The filters 223 can include SAW devices of aSAW component that includes any suitable combination of featuresdiscussed with reference to any embodiments discussed above.

The transceiver 224 can provide RF signals to the RF front end 222 foramplification and/or other processing. The transceiver 224 can alsoprocess an RF signal provided by a low noise amplifier of the RF frontend 222. The transceiver 224 is in communication with the processor 225.The processor 225 can be a baseband processor. The processor 225 canprovide any suitable base band processing functions for the wirelesscommunication device 220. The memory 226 can be accessed by theprocessor 225. The memory 226 can store any suitable data for thewireless communication device 220. The user interface 227 can be anysuitable user interface, such as a display with touch screencapabilities.

FIG. 21B is a schematic diagram of a wireless communication device 230that includes filters 223 in a radio frequency front end 222 and asecond filter 233 in a diversity receive module 232. The wirelesscommunication device 230 is like the wireless communication device 200of FIG. 21A, except that the wireless communication device 230 alsoincludes diversity receive features. As illustrated in FIG. 21B, thewireless communication device 230 includes a diversity antenna 231, adiversity module 232 configured to process signals received by thediversity antenna 231 and including filters 233, and a transceiver 234in communication with both the radio frequency front end 222 and thediversity receive module 232. The filters 233 can include one or moreSAW devices that include any suitable combination of features discussedwith reference to any embodiments discussed above. The diversity module232 and the radio frequency front end 222 can together be consideredpart of a radio frequency front end.

Although embodiments disclosed herein relate to surface acoustic wavefilters and/or resonators, any suitable principles and advantagesdisclosed herein can be applied to other types of acoustic wave devicesthat include an IDT electrode, such as Lamb wave devices and/or boundarywave devices. For example, any suitable combination of features of theacoustic velocity adjustment structures disclosed herein can be appliedto a Lamb wave device and/or a boundary wave device.

Any of the embodiments described above can be implemented in associationwith mobile devices such as cellular handsets. The principles andadvantages of the embodiments can be used for any systems or apparatus,such as any uplink wireless communication device, that could benefitfrom any of the embodiments described herein. The teachings herein areapplicable to a variety of systems. Although this disclosure includessome example embodiments, the teachings described herein can be appliedto a variety of structures. Any of the principles and advantagesdiscussed herein can be implemented in association with RF circuitsconfigured to process signals in a frequency range from about 30 kHz to300 GHz, such as in a frequency range from about 450 MHz to 8.5 GHz.Acoustic wave resonators and/or filters disclosed herein can filter RFsignals at frequencies up to and including millimeter wave frequencies.

Aspects of this disclosure can be implemented in various electronicdevices. Examples of the electronic devices can include, but are notlimited to, consumer electronic products, parts of the consumerelectronic products such as packaged radio frequency modules and/orpackaged filter components, uplink wireless communication devices,wireless communication infrastructure, electronic test equipment, etc.Examples of the electronic devices can include, but are not limited to,a mobile phone such as a smart phone, a wearable computing device suchas a smart watch or an ear piece, a telephone, a television, a computermonitor, a computer, a modem, a hand-held computer, a laptop computer, atablet computer, a microwave, a refrigerator, a vehicular electronicssystem such as an automotive electronics system, a stereo system, adigital music player, a radio, a camera such as a digital camera, aportable memory chip, a washer, a dryer, a washer/dryer, a copier, afacsimile machine, a scanner, a multi-functional peripheral device, awrist watch, a clock, etc. Further, the electronic devices can includeunfinished products.

Unless the context clearly requires otherwise, throughout thedescription and the claims, the words “comprise,” “comprising,”“include,” “including” and the like are to be construed in an inclusivesense, as opposed to an exclusive or exhaustive sense; that is to say,in the sense of “including, but not limited to.” The word “coupled”, asgenerally used herein, refers to two or more elements that may be eitherdirectly connected, or connected by way of one or more intermediateelements. Likewise, the word “connected”, as generally used herein,refers to two or more elements that may be either directly connected, orconnected by way of one or more intermediate elements. As used herein,the term “approximately” intends that the modified characteristic neednot be absolute, but is close enough so as to achieve the advantages ofthe characteristic. Additionally, the words “herein,” “above,” “below,”and words of similar import, when used in this application, shall referto this application as a whole and not to any particular portions ofthis application. Where the context permits, words in the above DetailedDescription using the singular or plural number may also include theplural or singular number respectively. The word “or” in reference to alist of two or more items, that word covers all of the followinginterpretations of the word: any of the items in the list, all of theitems in the list, and any combination of the items in the list.

Moreover, conditional language used herein, such as, among others,“can,” “could,” “might,” “may,” “e.g.,” “for example,” “such as” and thelike, unless specifically stated otherwise, or otherwise understoodwithin the context as used, is generally intended to convey that certainembodiments include, while other embodiments do not include, certainfeatures, elements and/or states. Thus, such conditional language is notgenerally intended to imply that features, elements and/or states are inany way required for one or more embodiments or that one or moreembodiments necessarily include logic for deciding, with or withoutauthor input or prompting, whether these features, elements and/orstates are included or are to be performed in any particular embodiment.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the disclosure. Indeed, the novel apparatus, methods, andsystems described herein may be embodied in a variety of other forms;furthermore, various omissions, substitutions and changes in the form ofthe methods and systems described herein may be made without departingfrom the spirit of the disclosure. For example, while blocks arepresented in a given arrangement, alternative embodiments may performsimilar functionalities with different components and/or circuittopologies, and some blocks may be deleted, moved, added, subdivided,combined, and/or modified. Each of these blocks may be implemented in avariety of different ways. Any suitable combination of the elements andacts of the various embodiments described above can be combined toprovide further embodiments. The accompanying claims and theirequivalents are intended to cover such forms or modifications as wouldfall within the scope and spirit of the disclosure.

What is claimed is:
 1. A multi-mode surface acoustic wave filtercomprising: a first interdigital transducer electrode on a piezoelectriclayer; an acoustic reflector on the piezoelectric layer; a secondinterdigital transducer electrode on the piezoelectric layer, the secondinterdigital transducer electrode longitudinally coupled to the firstinterdigital transducer electrode and positioned between the firstinterdigital transducer electrode and the acoustic reflector; and anacoustic velocity adjustment structure positioned over at least a gapbetween the first interdigital transducer electrode and the secondinterdigital transducer electrode, the acoustic velocity adjustmentstructure arranged to increase an acoustic wave propagation velocity ina first region that includes the gap relative to a second region over atleast a portion of the first interdigital transducer electrode.
 2. Themulti-mode surface acoustic wave filter of claim 1 wherein the acousticvelocity adjustment structure includes a high speed layer over the firstregion to increase the acoustic wave propagation velocity in the firstregion.
 3. The multi-mode surface acoustic wave filter of claim 2wherein the high speed layer includes a silicon nitride layer.
 4. Themulti-mode surface acoustic wave filter of claim 2 wherein the highspeed layer includes an aluminum oxide layer.
 5. The multi-mode surfaceacoustic wave filter of claim 1 further comprising a temperaturecompensation layer over the piezoelectric layer.
 6. The multi-modesurface acoustic wave filter of claim 5 wherein the acoustic velocityadjustment structure is at least partially embedded in the temperaturecompensation layer.
 7. The multi-mode surface acoustic wave filter ofclaim 5 wherein the acoustic velocity adjustment structure is at leastpartially disposed on the temperature compensation layer.
 8. Themulti-mode surface acoustic wave filter of claim 1 wherein the secondregion includes a first sub-region and a second sub-region, the firstsub-region defined over at least the portion of the first interdigitaltransducer electrode, the second sub-region defined over at least aportion of the second interdigital transducer electrode, and theacoustic wave propagation velocity in the first sub-region and theacoustic wave propagation velocity in the second sub-region beingapproximately the same.
 9. The multi-mode surface acoustic wave filterof claim 1 further comprising a third region over at least a portion ofthe acoustic reflector, the acoustic velocity adjustment structureincluding a low speed layer over the third region, the low speed layerconfigured to decrease the acoustic wave propagation velocity in thethird region relative to the second region.
 10. The multi-mode surfaceacoustic wave filter of claim 1 further comprising a third interdigitaltransducer electrode longitudinally coupled to the first interdigitaltransducer electrode such that the first interdigital transducerelectrode is positioned between the third interdigital transducerelectrode and the second interdigital transducer electrode.
 11. Themulti-mode surface acoustic wave filter of claim 10 further comprising asecond acoustic reflector longitudinally arranged such that the thirdinterdigital transducer electrode is positioned between the secondacoustic reflector and the first interdigital transducer electrode. 12.The multi-mode surface acoustic wave filter of claim 1 wherein the firstinterdigital transducer electrode and the second interdigital transducerelectrode have a pitch variation of no greater than 5 percent.
 13. Themulti-mode surface acoustic wave filter of claim 1 wherein the firstregion includes a portion of the first interdigital transducerelectrode, wherein the portion of the first interdigital transducerelectrode is less than one third of a length of the first interdigitaltransducer electrode along a direction perpendicular to an aperturedirection.
 14. A radio frequency module comprising: a filter including amulti-mode surface acoustic wave filter having a first interdigitaltransducer electrode on a piezoelectric layer, an acoustic reflector onthe piezoelectric layer, a second interdigital transducer electrode onthe piezoelectric layer, and an acoustic velocity adjustment structurepositioned over at least a gap between the first interdigital transducerelectrode and the second interdigital transducer electrode, the secondinterdigital transducer electrode longitudinally coupled to the firstinterdigital transducer electrode and positioned between the firstinterdigital transducer electrode and the acoustic reflector, theacoustic velocity adjustment structure arranged to increase an acousticwave propagation velocity in a first region that includes the gaprelative to a second region over at least a portion of the firstinterdigital transducer electrode; and a radio frequency circuit elementcoupled to the filter, the filter and the radio frequency circuitelement being enclosed within a common module package.
 15. The radiofrequency module of claim 14 wherein the radio frequency circuit elementis a radio frequency amplifier arranged to amplify a radio frequencysignal.
 16. The radio frequency module of claim 14 wherein the radiofrequency circuit element is a switch configured to selectively couplethe filter to a port of the radio frequency module.
 17. A wirelesscommunication device comprising: a filter including a multi-mode surfaceacoustic wave filter having a first interdigital transducer electrode ona piezoelectric layer, an acoustic reflector on the piezoelectric layer,a second interdigital transducer electrode on the piezoelectric layer,and an acoustic velocity adjustment structure positioned over at least agap between the first interdigital transducer electrode and the secondinterdigital transducer electrode, the second interdigital transducerelectrode longitudinally coupled to the first interdigital transducerelectrode and positioned between the first interdigital transducerelectrode and the acoustic reflector, the acoustic velocity adjustmentstructure arranged to increase an acoustic wave propagation velocity ina first region that includes the gap relative to a second region over atleast a portion of the first interdigital transducer electrode; anantenna operatively coupled to the filter; a radio frequency amplifieroperatively coupled to the multi-mode surface acoustic wave filter andconfigured to amplify a radio frequency signal; and a transceiver incommunication with the radio frequency amplifier.
 18. The wirelesscommunication device of claim 17 further comprising a baseband processorin communication with the transceiver.
 19. The wireless communicationdevice of claim 17 wherein the filter is included in a radio frequencyfront end.
 20. The wireless communication device of claim 17 wherein thefilter is included in a diversity receive module.